Security measures are needed for businesses, government agencies and buildings, transportation and high traffic areas. One of the most common security implementations is the use of a camera to provide continuous, periodic, or on-demand surveillance of a targeted area. Additionally, cameras are often used for object recognition, and determining the position, size or dimensional measurement of objects.
By using information associated with the positioning of a camera, including the height of a camera above the surface that it monitors, and the angle of the line-of-view of the camera formed with a perpendicular line to the target surface, accurate estimates of size, length, and distance between objects can be calculated. Camera angle measurement techniques are known. Many surveillance cameras can self-determine the camera angle relative to a vertical or horizontal standard. The height measurement of a surveillance camera can be achieved in a variety of ways.
The height of a camera can be physically measured using measuring tape, calibrated telescoping poles or laser measurement devices. These are typically time-consuming techniques and may require expensive measurement and access equipment. Relocation, adjustment, or replacement of the camera may require repeating these measurement efforts.
Alternatively, a satellite positioning system, such as the global positioning system (GPS), may be added or incorporated with the camera. Cameras enabled or outfitted with GPS capability can report their height (or elevation compared to a reference model point such as sea level) as well as position, however, GPS-enabled cameras may have accuracy issues that detract from the use of the surveillance camera for accurate measurement. There may also be significant cost impacts for the purchase of GPS-enabled cameras or the purchase and effort of outfitting existing cameras with GPS devices.
Techniques are known to calculate the height of an elevated surveillance camera from knowledge of the viewing/tilt angle of the camera, knowledge of the known height of an object, such as a person in the camera viewing area, and the apparent height of the person as imaged by the camera. Other techniques are known that make use of distance detection devices to measure the distance to an object in the camera field of view and the tilt angle of the camera to determine the height of the elevated camera, or use calibration techniques making use of vanishing points and vanishing lines within the camera viewing field. Still other techniques use a plurality of coordinate data of the feet and heads of humans imaged in the camera viewing area, and use averages to determine camera height by substituting the coordinate data into a relation that includes: camera focal distance, camera angle, the average height of humans imaged, and an initial camera height.
These known techniques require additional equipment, such as distance detection or GPS devices, prior calibration, known object size of an imaged object, or elaborate coordinate systems to accurately calculate the height of an elevated surveillance camera. An objective of the present invention is to enable calculation of the height of a surveillance camera with improved accuracy, reduced sampling and without the need for additional equipment, calibration or prior height knowledge of an imaged object.